This invention relates to the field of air bag deployment systems for an automotive vehicle and more particularly to the area of an air bag deployment chute that is bonded to the underside of an instrument panel substrate.
FIG. 1 illustrates a prior art configuration of an air bag deployment system 100 in which an air bag deployment chute 150, having a flange 152, is bonded to the underside of an instrument panel substrate 120. Chute 150 is a one piece molded structure that contains several apertures 155 into which hooks 180 extending from an air bag container is attached. Although not shown, the air bag container is permanently attached to the vehicle structure. Hooks, such as 180, together with the air bag container perform the task of restraining the instrument panel 100 and the air bag deployment chute 150 from movement during air bag deployment. In such a manner, most all energy from the deploying air bag is directed outward to cause the pre-weakened seams 102 that form the deployment door 110 to fracture and allow release of the air bag from its container.
Instrument panel base substrate 120 contains a pre-weakened seam 102 that, depending on the outer layers, may extend through the base and in some cases partially through the upper layers to provide a desired invisible seam. In this illustration, air bag chute 150, foam layer 130 and outer layer of a class “A” skin 140 are all formed of TPO (Thermoplastic Olefin) materials to facilitate recycling. As such, only the base substrate 120 needs to be scored or otherwise formed to be undercut in the tear seam path that defines the deployment door. The layers 130 and 140 are typically bonded together with adhesives or the like. However, the bonding of the flange 152 of deployment chute 150 to the underside of the substrate 120 is typically performed via ultrasonic welding. In such bonding, ribs 154, 156, 158, 160, etc. are integrally formed in the upper surface portion of flange 152. When welded to the underside of substrate 120, a small gap 166 often remains between the flange 152 and substrate 120 due to the volume of the melted ribs.
Air bag 170 is shown in FIG. 1 as beginning its deployment. Arrows are used to represent the side forces developed against the air bag side wall 172 due to the expanding gas that is generated to inflate the air bag against internal wall 151 of the deployment chute 150. In the configuration of FIG. 1, the air bag 170 fabric is shown as diverting around the upper corner 153 of internal wall 150 and into the gap 166. When this occurs, excessive pressure can be generated on the weld 154 that may cause fracturing of the weld bond between flange 152 and substrate 120, before the door seam 102 fractures and allows the air bag to fully deploy. It is also believed that the side wall 151 of chute 150 may be slightly expanded during this early stage of deployment that, in turn, may cause corner 153 to be lowered and gap 166 to be enlarged and therefore allow the air bag 170 fabric to further migrate towards the weld 154.